Enhancing the electrochemical performance of next-generation 5 V class Li-ion batteries using LiPF6/LiBOB mixed salt electrolyte

Abstract

Modification of LiPF₆-based electrolytes by simply combining two lithium salts to obtain a mixed electrolyte has been demonstrated as a potential strategy for the next-generation 5 V class lithium-ion battery, hindered by electrolyte decomposition and transition metal dissolution. In this study, LiPF₆/LiBOB mixed salt electrolyte with different LiBOB content (10% and 20%) in EC/DEC/DMC at a ratio of 1:1:1 (v/v) was tested in the high-voltage LiNi_0.5Mn_1.5O₄ (LNMO) cathode to optimize their electrochemical performances. The mixed salt electrolyte performed higher ionic conductivity and better stability window than the baseline LiPF₆ electrolyte. A series of electrochemical measurements, including EIS, CV, and CD, are performed in the half-cell configuration with Li-metal. LiPF₆ electrolytes with 10% LiBOB showed higher discharge capacity up to 133.5 mAh g^-1, better cycle stability up to 1C, and remained stable after 25 cycles. The improved performance of the mixed salt electrolyte can be attributed to the surface-forming ability of LiBOB in providing a stable (Cathode-Electrolyte Interface (CEI) layer. In our finding, the synergistic effect between LiPF₆ and LiBOB has a certain optimal ratio in which the higher ratio of up to 20% tends to decrease the overall electrochemical performance of the high-voltage LNMO cathode.